Structures for South Pelaw Junction

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John Donnelly
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Structures for South Pelaw Junction

Postby John Donnelly » Mon Jul 02, 2018 7:32 am

Whilst the layout itself exists as nothing more than a Templot plan, I've made a start on one of the structures, the bridge at the Washington end of the junction.

One pier is almost complete (with individual stones) and the shell of another has been built along with a start on one of the spans:

Image

and the real thing:

Image

John

pete55
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Re: Structures for South Pelaw Junction

Postby pete55 » Mon Jul 02, 2018 8:32 pm

Looks terribly familiar to my eyes John!
Nice stonework coming along too....the cast iron panels above the girder spans are an interesting challenge too.

Keep up the good work

Pete

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Mon Jul 02, 2018 9:19 pm

pete55 wrote:Looks terribly familiar to my eyes John!
Nice stonework coming along too....the cast iron panels above the girder spans are an interesting challenge too.

Keep up the good work

Pete


Cheers Pete, thought you might recognise it...

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Wed Jul 04, 2018 4:58 pm

I've just textured the stones with a ball cutter in a Dremel, slapped a very quick coat of paint on and I'm now much happier with the way the stonework looks.

Image

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Thu Jul 05, 2018 8:18 pm

Lots of progress tonight and the pier is getting close to completion. The capping stone has been added and the stones have been painted and weathered. Paint is Vallejo Acrylics with a wash of Mig Brown for Dark Green. After each application of the wash, individual stones have been picked out in the original colour then washed over again to provide some variety.

Image

Image

Image

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Tue Jul 17, 2018 10:46 pm

Its beginning to look a lot like a bridge...

I've completed the main girder structures (details still to add) and positions on the piers still need some slight adjustment.  

Unfortunately, everything I've posted already had to be scrapped when I realised that I'd made the bridge 6mm too narrow and, on such a narrow bridge, I decided I couldn't live with the difference.

Image

Image

Image

pete55
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Re: Structures for South Pelaw Junction

Postby pete55 » Wed Jul 18, 2018 8:45 am

Certainly looking the part.....you'll soon need a baseboard or three at this rate!

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Wed Jul 18, 2018 9:39 am

Cheers Pete, you may be right about the baseboards :D

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Fri Jul 20, 2018 8:33 am

Detailing of the bridge girders, 'bolts' (50 of them on this one section) cut from 1mm round styrene strip.

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Noel
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Re: Structures for South Pelaw Junction

Postby Noel » Fri Jul 20, 2018 9:40 am

John, not a bridge I have any knowledge of, but it looked interesting, so I looked at the photos on your South Pelaw Junction website. The visible parapet beams appear to be cast iron, rather than built-up wrought iron; presumably the whole bridge used cast iron and survived as long as it did because it saw only limited use? I did notice from the photographs that the webs on the lower girders appear to be much deeper than those on the top ones - not surprising as the lower ones are loadbearers, while the top ones just provide a parapet to retain the surfacing, and stop people falling off, and appear to be mounted on the outside edge of the main beams.

I don't know the implication of your having put 'bolts' in quotes, but they were almost invariably rivets, which showed a domed head both sides; bolts will tend work loose under vibration.

And now I should probably head for cover ;) .
Noel

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Re: Structures for South Pelaw Junction

Postby Armchair Modeller » Fri Jul 20, 2018 10:12 am

Having studied Cumbrian cast iron viaducts etc. recently in some detail, I am sure that bolts were used on occasion. ;)

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John Donnelly
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Re: Structures for South Pelaw Junction

Postby John Donnelly » Fri Jul 20, 2018 10:13 am

Thanks for the comments Noel, being ignorant of such thing, they are much appreciated.

The bridge, in earlier days, carried a farm track and, later was used just as a footbridge. The railway was gone by 1985 but the bridge survived until about 4 years ago when it was demolished and completely removed in a little over 24 hours.

Rivets does make more sense but, with over 300 of them to add, I can live without them being domed :mrgreen:

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Noel
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Re: Structures for South Pelaw Junction

Postby Noel » Fri Jul 20, 2018 2:36 pm

It's long out of print, but if you can obtain a copy of "Bridges for Modellers", L V Wood, OPC 1985, ISBN 0-86093-226-5, or access to one, it's very enlightening.
Noel

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Noel
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Re: Structures for South Pelaw Junction

Postby Noel » Fri Jul 20, 2018 3:53 pm

Armchair Modeller wrote:Having studied Cumbrian cast iron viaducts etc. recently in some detail, I am sure that bolts were used on occasion.


According to L T C Rolt they were used in the pillars of the Tay Bridge completed in 1878 by Thomas Bouch, as were gib and cotter joints for the bracing. Meldon http://www.southdownswalking.com/wp-content/uploads/2015/10/Yes-Tor-Meldon-Viaduct-61-e1446033767816.jpg and Crumlin http://map.coflein.gov.uk/index.php?action=do_details&numlink=34959 seem to have been mostly rivetted at least, but clearly have some bolts. Beyond that I don't know, but I suspect that it is relevant that these and the ones you have been looking at were truss girders. Photographs of built up plate girders only seem to show rivets. The two links above suggest that their built up sections were rivetted, but may have been attached to other sections with bolts.
Noel

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Re: Structures for South Pelaw Junction

Postby Armchair Modeller » Fri Jul 20, 2018 4:42 pm

I don't disagree with your general summary Noel. In any case, the photos and drawings I have seen only give limited information.

In very general terms, I suspect rivets were used to create sub-assemblies and bolts to assemble the large sub-assemblies together on the viaducts I was looking at - and yes you are correct that the girders in these are different to what John is building.

He seems happy, in any case, which is the important thing ;)

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Re: Structures for South Pelaw Junction

Postby pete55 » Tue Aug 21, 2018 6:52 pm

The cast iron panels on this bridge used nuts and bolts, both to fasten to each other and onto the supporting girders they stood on.
Remind me John to lend you the detail pics taken a year or so before demolition.

Pete

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Noel
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Re: Structures for South Pelaw Junction

Postby Noel » Wed Aug 22, 2018 11:27 am

Pete's post led me to investigate further, which demonstrated that cast iron was always bolted, not rivetted. I haven't found a definite reason, but I assume it relates to cast irons' poor ability to cope with high temperatures and its brittleness under impact. Hot riveting would therefore be likely to cause serious damage to cast iron beams. I was aware of the differences between cast and wrought iron, but had not considered the implications in this context, so thanks, Pete.
Noel

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Re: Structures for South Pelaw Junction

Postby Crepello » Wed Aug 22, 2018 3:44 pm

Don't rivets also expand in girth within their holes as they are closed? This would put tensile hoop stresses around the hole, which is a bad idea with cast iron, as it is relatively weak in tension.

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Noel
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Re: Structures for South Pelaw Junction

Postby Noel » Wed Aug 22, 2018 5:41 pm

Wouldn't expansion of the rivet produce compression stresses?
Noel

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Le Corbusier
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Re: Structures for South Pelaw Junction

Postby Le Corbusier » Wed Aug 22, 2018 6:34 pm

Noel wrote:Wouldn't expansion of the rivet produce compression stresses?

That was certainly my understanding .... I understood that hoop stresses related to pipes etc where the outer skin is in tension?
Tim Lee

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Re: Structures for South Pelaw Junction

Postby Terry Bendall » Wed Aug 22, 2018 7:21 pm

Noel wrote:It's long out of print, but if you can obtain a copy of "Bridges for Modellers", L V Wood, OPC 1985, ISBN 0-86093-226-5, or access to one, it's very enlightening.


I have not looked at this thread for a while but in the absence of anything else the CD A Modeller's Guide to Civil Engineering Structures published by the Scalefour Society and available from our stores might be useful. There is a lot of useful information about cast iron bridges and much else besides.

Terry Bendall

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Re: Structures for South Pelaw Junction

Postby grovenor-2685 » Wed Aug 22, 2018 9:08 pm

Noel wrote:Wouldn't expansion of the rivet produce compression stresses?

Action and reaction, compression in the rivet has to be resisted by tension in the surrounding metal, otherwise it will distort (or crack).
Regards

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Noel
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Re: Structures for South Pelaw Junction

Postby Noel » Thu Aug 23, 2018 11:20 am

I think I follow you, Keith, though it's straining my elementary knowledge of physics! If I've got it right, the material being rivetted undergoes compression forces radially to the hole, and tension forces tangentially to it resulting from the forces acting to enlarge the hole?
Noel

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Simon_S
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Re: Structures for South Pelaw Junction

Postby Simon_S » Thu Aug 23, 2018 12:50 pm

There should be clearance between the rivet and the hole after the rivet head has been formed. The rivet's job is to create friction between the parts being joined by pulling them together, not to align or reinforce the joint.

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Le Corbusier
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Re: Structures for South Pelaw Junction

Postby Le Corbusier » Thu Aug 23, 2018 1:05 pm

Simon_S wrote:There should be clearance between the rivet and the hole after the rivet head has been formed. The rivet's job is to create friction between the parts being joined by pulling them together, not to align or reinforce the joint.

Wouldn't that be similar to a bolt? What merit does one have over the other?
Tim Lee


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